The invention relates generally to the field of micro-electro-mechanical-systems (MEMS). In particular, the invention relates to a multi-axis magnetically actuated micromechanical device.
Micro-electro-mechanical-systems (MEMS) are microdevices that are batch-fabricated using micromachining techniques that combine electrical and/or magnetic components with mechanical components. MEMS have several attractive properties. They are small, low in mass and cost little to produce. In one class of MEMS, the microdevice consists of a plate that is suspended by two torsional flexures, or bars, which define an axis about which the plate can rotate. This class of MEMS has a range of applications. In particular, such single axis MEMS devices may be employed as micro-mirror mounts. Micro-mirrors are useful in a variety of optical scanning applications, such as holographic systems, robot vision systems, security systems, video displays, heads-up displays, video cameras, retinal projector displays, laser scanning microscopes and laser detection and ranging systems (LIDAR), and a variety of optical switch applications, such as routing switches, matrix switches, and multiplexers. However, such systems typically require optical scanning, or optical switching, in two orthogonal directions. One method of achieving scanning, or switching, in two orthogonal directions is to place two or more single axis MEMS devices in series. However, a serial arrangement of mirrors always produces optical aberrations of the scanned image. In addition, geometric considerations seriously limit the matrix dimensions of optical matrix switches that employ serial mirror arrangements.
Another method of achieving two orthogonal direction switching, such as that desired in a matrix switch, is to employ electronic switches that perform optical-to-electrical and electrical-to-optical signal conversion. These signal conversions, however, introduce bandwidth limitations, conversion losses, and signal degradation. Another method of achieving two orthogonal direction switching employs an integrated optical waveguide circuit. Waveguide circuits, however, are difficult to expand to large matrix dimensions because waveguide architectures typically require many signal paths to cross one another. Such crossings lead to waveguide cross-talk, signal losses, and require complicated switching algorithms.
Another method of achieving two orthogonal direction scanning is to employ a biaxial, or two-axis, MEMS device. Such a device may consist of a inner plate suspended by two bars, defining one axis of rotation, which are attached to an outer plate that is in turn suspended by two bars that define another, orthogonal, axis of rotation. Several methods are known to actuate the rotational motion of the plates. One method of actuation is by piezoelectric drive. However, piezoelectric drive requires the use of linkages and coupling mechanisms to transfer the motion to the plates. Accordingly, geometric considerations make it difficult to transfer piezoelectric motion to the nested plates of a two-axis MEMS device. Further, it is often difficult to match the low mechanical impedance of a rotatable plate to the high impedance of a typical piezoelectric actuator, such as a stack or length extender bar. Another method actuates the rotation electrostatically. However, electrostatic actuation requires the use of high voltages (hundreds, or thousands, of volts) to achieve large angular deflection (greater than 20 degrees) of plates larger than about one millimeter square. Such high voltages are not readily compatible with standard CMOS and battery operated equipment. Electrostatic actuation is also highly nonlinear and, as a result, the plate can xe2x80x9csnap downxe2x80x9d if over-actuated and reduce angular precision. Consequently, current two-axis MEMS devices suffer from the inability to provide large angular deflection of xe2x80x9clargexe2x80x9d rotational elements in a compact device with operational voltages that are readily compatible with standard device logic and other devices.
The invention, in one embodiment, provides a multi-axis magnetically actuated device capable of high angular deflection about each axis without the necessity of high actuation voltages. In one aspect, the invention provides a small, lightweight two-axis micromechanical device which has a high torque and a high bandwidth about both axes. In another aspect, a two-axis magnetically actuated micromechanical device of the invention provides a useful two-axis optical micro-mount. A wide variety of optical elements can benefit from being mounted on a two-axis mount including, for example, photodetectors, diffraction gratings, reflectors, mirrors, prisms, and optical beam steering elements in general. The embodiments of a micromechanical device of the invention have a wide range of applications, including, but not limited to, optical scanning applications, optical switch applications, and image sensing applications. For example, the invention is useful in such optical scanning applications as holographic systems, robot vision systems, security systems, video displays, heads-up displays, video cameras, retinal projector displays, bar code scanning, laser scanning microscopes and LIDAR. Embodiments of the invention can provide several advantages to an optical scanning application, such as, fast two-dimensional scanning of relatively large mirror elements over large scan, or deflection, angles with high angular precision without the optical aberrations inherent to serial mirror configurations. According to another aspect, the invention provides a device that is compact and that operates with voltages that are readily compatible with other devices and standard device logic.
The invention is useful in such optical switch applications as, for example, series bus access couplers, optical routing switches, optical matrix switches, packet routers, optical logic circuits, reconfigurable networks, and multiplexers such as add-drop multiplexers and space division multiplexers. According to other aspects, optical switches of the invention are also useful in, for example, optical communication network, optical gyroscope, and optical signal processing applications. Embodiments of the invention can also provide several advantages to an optical switch application, including, for example, a compact, scalable, fast response, multiple wavelength, intelligently routable, switching element that can achieve a multitude of stable switching states and which returns to a known state upon removal or loss of power. In addition, the optical switch of the invention achieves these advantages without a time-consuming light-to-electricity-to-light conversion process and without the optical aberrations inherent to serial mirror configurations.
In one embodiment, the invention provides a two-axis magnetically actuated micromechanical device capable of angular deflections of a plate, or rotational member, of up to 45xc2x0. According to one aspect, the two-axis magnetically actuated device comprises two nested rotational members, an inner rotational member nested within an outer rotational member that in turn is nested within a base member. The inner rotational member is mounted by two inner torsional flexures to the outer rotational member that in turn is mounted by two outer torsional flexures to the base member. The inner torsional flexures define an inner axis of rotation while the outer torsional flexures define an outer axis of rotation substantially orthogonal to the inner axis. The rotational motions of each rotational member arise in response to an interaction between a magnetic influence, such as a non-uniform external magnetic field, and a magnetic moment generated by a current passing through coils arranged adjacent to a surface of the inner rotational member. Bulk micromachining techniques enable the members to be formed from a monolithic silicon wafer and can produce a member with a smooth surface. The smooth surface of a member may function as a reflector. In one embodiment, the inner rotational member functions as a reflector. Accordingly, in one embodiment the invention provides a two-axis magnetically actuated micromechanical mirror. In another embodiment, the invention provides an inner rotational member that functions as a diffraction grating.
In another embodiment, the invention provides a two-axis magnetically actuated device further comprising a magnet and at least one pole piece. The two-axis magnetically actuated device comprises two nested rotational members, an inner rotational member nested within an outer rotational member that in turn is nested within a base member. The inner rotational member is mounted by two torsional flexures, defining an inner axis of rotation, to the outer rotational member that in turn is mounted by two torsional flexures to the base member, these flexures defining an outer axis of rotation which is substantially orthogonal to the inner axis. Two pairs of coils are arranged adjacent to a surface of the inner rotational member such that application of a current to a coil generates a magnetic moment substantially perpendicular to the surface of the inner rotational member. The magnet and pole piece(s) are arranged to produce a magnetic field gradient across the inner rotational member. Accordingly, the magnet and pole piece(s) are arranged to produce a non-uniform external magnetic field, i.e., a magnetic influence, for interaction with a magnetic moment generated by the coils and thereby actuate a rotational movement of the inner and/or outer rotational members.
In one aspect, the invention provides a device comprised of an array of two-axis magnetically actuated devices. In another aspect, the invention provides an optical switch comprised of a two-axis magnetically actuated device. In a further aspect, the invention provides a compact optical switch adapted for simultaneous independent alignment and full Nxc3x97N optical switch functionality.
According to another embodiment, the invention provides a method of actuating a multi-axis magnetically actuated device. One such method of actuation includes applying an electric current to a first set, or pair, of coils arranged adjacent to a surface of the inner rotational member to induce a rotational movement of the outer and inner rotational members about the outer axis in response to interaction with a first magnetic influence and, applying an electrical current to a second set, or pair, of coils also arranged adjacent to the surface of the inner rotational member to induce a rotational movement of the inner rotational member about the inner axis in response to interaction with a second magnetic influence.
According to a further embodiment, the invention provides a method of fabricating a multi-axis magnetically actuated device. In one such method of fabrication, a two-axis magnetically actuated micromechanical device is micromachined from a monolithic silicon-on-insulator (SOI) wafer and coils formed by electroplating a metal layer onto an adhesion layer sputtered on the silicon wafer. In this embodiment, the outer rotational member, inner rotational member, and flexures are formed substantially by micromaching techniques such as, for example, photolithography and etching techniques. In another embodiment, a two-axis magnetically actuated device is micromachined from a monolithic SOI wafer and coils formed from wound wire that are incorporated into the inner rotational member. In another embodiment, a two-axis magnetically actuated device is machined, molded and/or stamped from a combination of plastic, metal, silicon, and/or ceramic components and coils formed from wound wire that are incorporated into the inner rotational member.